1. Field
The present disclosure relates generally to aerial surveys and, in particular, to aerial surveys of forests. Still more particularly, the present disclosure relates to a method and apparatus for performing a forest inventory through an aerial survey.
2. Background
Forestry management is a branch of forestry that includes many different aspects. These aspects may include environmental, economic, administrative, legal, and social aspects of managing a forest. Forestry management may consist of various techniques such as timber extraction, planting trees, replanting trees, cutting roads and pathways through forests, preventing fires in a forest, maintaining the health of the forest, and other suitable activities.
When performing these and other operations with respect to forest management, collecting information about the forest may be desired. For example, collecting information about the forest provides an ability to analyze the state of the forest as well as identify missions that may be performed. These missions may include, for example, at least one of replanting trees, harvesting trees, thinning the forest to improve growth, applying fertilizer, performing pest removal, generating warnings of potential fire conditions, initiating fire risk reduction activities, removing dead wood, reducing forest floor undergrowth, performing timber improvement activities, and other suitable operations.
In obtaining information about a forest, aerial surveys may be performed as part of a forest inventory mission to identify information about a forest. A forest inventory mission may be a mission configured to identify information about a forest for assessment or analysis. This information may be used to identify types of trees, height of trees, age of trees, health of trees, forest boundaries, and other suitable information about trees in the forest. For example, a number of trees per acre may be identified through a forest inventory mission.
Additionally, a forest inventory mission also may be used to identify other information about vegetation, wildlife, or both vegetation and wildlife within a forest. A forest inventory mission may also show a presence of dead or decaying trees. In this case, information about dead or decaying trees may indicate a pest problem. Moreover, a forest inventory mission may be configured to identify boundaries of the forest.
Aerial surveys may be performed using at least one of manned aerial vehicles or unmanned aerial vehicles. As an example, an unmanned aerial vehicle may fly over a forest to generate information about the forest for a forest inventory mission. The unmanned aerial vehicle may include a light detection and ranging (LiDAR) system and a camera system. The light detection and ranging system may be used to send light in the form of a laser beam toward the forest.
Currently, an aerial vehicle is flown a route by a pilot that takes the aerial vehicle over different locations in a forest. These locations are selected such that the aerial vehicle can generate information about all or a portion of the forest. The aerial vehicle scans a location with a laser beam using a light detection and ranging system. The light detection and ranging system measures the distance to points in the forest by measuring the time light takes to return to the light detection and ranging system. From these measurements, the light detection and ranging system may generate information about locations in the forest.
The responses to the laser beam detected by the light detection and ranging system are used to generate a point cloud for the forest. This point cloud may be used to generate information such as canopy height, crown volume estimates, density of trees, and other important information.
In performing these types of aerial surveys, cost is one factor that may affect when and how often aerial surveys are performed. The cost of sending one or more aerial vehicles to generate a point cloud for different locations in a forest often is significant. To make the performance of an aerial survey more economical, large areas are surveyed each time an aerial survey is performed. For example, when an aerial survey is performed, about 50,000 or more acres are surveyed to reduce the cost per acre for performing an aerial survey.
Further, the aerial surveys are typically performed at some safe height above terrain, and around obstacles and clouds that may be present. When obstacles are present, the unmanned aerial vehicle may need to fly higher over the forest. As the height of the unmanned aerial vehicle over the area being surveyed increases, the density of the point cloud generated by the aerial survey may decrease. As a result, when an aerial survey is performed, the level of resolution of the point cloud from information that can be gathered for a forest may not be as high as desired.
Further, at these higher heights, cloud cover may obstruct the laser used to perform an aerial inventory. For example, a cloud may cause the laser to be reflected, refracted, or be otherwise directed away from the forest to be surveyed. When the laser is reflected or refracted, the responses detected by the light detection and ranging system may be inaccurate because the responses may be those from the clouds rather than the forest. As a result, the information in a point cloud for a forest may have gaps where a location is covered by a cloud when an aerial survey is performed.
Additionally, due to the cost of conducting a forest inventory mission, it is often only economical to survey the forest at irregular intervals in time. Thus, long periods of time lapse between surveys of a forest. For example, a forest may only be surveyed after long periods of time such as four years due to personnel limitations, equipment limitations, and cost of an aerial survey. A location that is missed during one survey because of cloud cover may not be resurveyed for another four years. As a result, an eight year gap may be present between the collection of information for a particular location in a forest.
Currently, one manner in which the gaps in information generated by the aerial survey may be reduced is by careful scheduling of the aerial survey. For example, an aerial survey is typically only performed when the cloud cover over the forest is nonexistent or below a certain percentage. As a result, selecting times when cloud cover is nonexistent or sufficiently low to obtain a desired amount of information may reduce issues in gaps in information generated because of the presence of cloud cover. If weather conditions result in the cloud cover changing to have clouds that cover more of the forest than desired, the aerial survey may be rescheduled to another time when the clouds in the cloud cover obscuring the forest is at a thin enough level to generate the information with a desired level of quality.
Although rescheduling an aerial survey to a time when the cloud cover is sufficiently low may allow for gathering a desired amount of information about the forest, the rescheduling of the aerial survey may be more costly than desired. Oftentimes, rescheduling an aerial survey may increase the cost of performing the aerial survey.
Furthermore, operators of aircraft that perform surveys using light detection and ranging systems may have different amounts of demand based on the season of the year. For example, a higher demand may be present in summer months when cloud cover is less common as compared to winter months. These peaks and troughs in demand for aerial surveys using aircraft with light detection and ranging systems may increase average prices for such services in regions where cloud cover is more frequent.
Additionally, the cost for performing aerial surveys using aircraft with light detection and ranging systems may vary over different geographic regions. For example, the cost to perform an aerial survey of a forest in Seattle may be more expensive than to perform a similar survey of a forest in Texas. The amount of cloud cover in Seattle may lead to greater seasonal spikes and troughs in demand for performing aerial surveys using aircraft with light detection and ranging systems.
Another solution involves the unmanned aerial vehicle flying below the clouds in the cloud cover. Flying at these lower levels may result in the unmanned aerial vehicle encountering more weather conditions that may be hazardous to the vehicles and reduce the field of view of the sensor. Further, the unmanned aerial vehicle may encounter increased obstructions such as power lines, rock outcroppings, cell towers, and other types of obstructions when flying at lower levels below the cloud cover.
Moreover, in populated areas, a low-flying unmanned aerial vehicle may raise privacy concerns with individuals in the area being surveyed. Flying the unmanned aerial vehicle at lower levels may also result in a reduced surface area of the scan as compared to flying the unmanned aerial vehicle at a higher altitude. For example, for each 10 percent reduction in altitude, the amount of time needed to complete an aerial survey increases by about 10 percent.
Although the resolution of the point cloud may increase with the lower altitude, the efficiency with respect to time decreases. In other words, flying at lower altitudes may result in more time needed to generate the point cloud. This additional time may increase the cost of the aerial survey, which is an increase in expense that is unwarranted if the additional resolution in the point cloud is not desired.
In some cases, multiple unmanned aerial vehicles may be used to perform the aerial survey when performing aerial surveys at lower altitudes. The additional unmanned aerial vehicles may be used to cover all of the forest and keep the performance of the aerial survey within a limited timeframe. Longer timeframes may result in cloud cover occurring which may reduce the coverage of the aerial survey.
Additionally, flying at lower altitudes may result in increased risk for icing conditions and turbulence. With these conditions, the times at which aerial surveys may be performed may become more limited. For example, even though clouds may be absent, these conditions at lower altitudes may also prevent the performance of an aerial survey. Thus, aerial surveys performed at lower altitudes may end up being more costly than desired as compared to aerial surveys performed at higher altitudes above the clouds.
Therefore, it would be desirable to have a method and apparatus that takes into account at least some of the issues discussed above, as well as other possible issues.